The SARS-CoV-2 Nsp3 macrodomain reverses PARP9/DTX3L-dependent ADP-ribosylation induced by interferon signaling

SARS-CoV-2 nonstructural protein 3 (Nsp3) contains a macrodomain that is essential for coronavirus pathogenesis and is thus an attractive target for drug development. This macrodomain is thought to counteract the host interferon (IFN) response, an important antiviral signalling cascade, via the reversal of protein ADP-ribosylation, a posttranslational modification catalyzed by host poly(ADP-ribose) polymerases (PARPs). However, the main cellular targets of the coronavirus macrodomain that mediate this effect are currently unknown. Here, we use a robust immunofluorescence-based assay to show that activation of the IFN response induces ADP-ribosylation of host proteins and that ectopic expression of the SARSCoV- 2 Nsp3 macrodomain reverses this modification in human cells. We further demonstrate that this assay can be used to screen for on-target and cell-active macrodomain inhibitors. This IFN-induced ADP-ribosylation is dependent on PARP9 and its binding partner DTX3L, but surprisingly the expression of the Nsp3 macrodomain or the deletion of either PARP9 or DTX3L does not impair IFN signaling or the induction of IFNresponsive genes. Our results suggest that PARP9/DTX3Ldependent ADP-ribosylation is a downstream effector of the host IFN response and that the cellular function of the SARSCoV- 2 Nsp3 macrodomain is to hydrolyze this end product of IFN signaling, rather than to suppress the IFN response itself

Countrywide Computer Alerts to Community Physicians Improve Potassium Testing in Patients Receiving Diuretics

More than 20% of approximately 35,000 patients filling a diuretic prescription had no potassium blood test recorded within the previous year. A laboratory reporting system used throughout Israel by Maccabi Healthcare Services physicians was modified to provide physician alerts regarding potassium testing. The physicians were experienced users of a computerized medical record (CMR) that provided online laboratory test results. A nightly batch file checked pharmacy diuretic purchases against the patient's potassium blood test status. On-screen computer-generated reminders were sent to physicians of patients lacking a recent potassium test. Reminders to clinicians increased potassium testing by 9.8% (p < 0.001). Physician age and gender played a small part in predicting compliance to the alert, but specialty and practice size did not. The time delay between the date a reminder was sent and the potassium test date decreased steadily during the intervention. The success of this reminder system encourages expansion to include more drug–laboratory interactions. Furthermore, direct alerts to patients at multiple organization/patient contact points are planned